With introduction of high luminosity LED and well developed technology of white light LED, LED illumination products adopted for desk lamps, projection lamps and the like also have been developed that are very likely to replace the conventional incandescent lamps in the future to become the main lighting sources of indoor illumination. Most conventional LED driving circuits adopt a Charge-Pump circuit mode or a Boost-Buck circuit mode. These two types of driving circuits still leave a lot to be desired as far as efficiency is concern.
Take the charge-pump circuit mode for instance. Its efficiency curve is averaged at 60-70%, and might be as low as 50%. It also provides a limited range of output voltage (limited to two times of input voltage). To drive multiple LEDs, the LEDs have to be coupled in parallel, and current-limit resistors have to be added to prevent uneven current and uneven illumination. As a result, the cost is higher, and more energy is wasted on the additional elements, and efficiency also is lower. On the other hand, the boost-buck circuit mode adopts inductors that make circuit design more complicated. To drive multiple LEDs the high cost inductors have to withstand a greater current during energy transformation. Hence it also is not a desirable LED driving circuit. How to provide a more efficient driving circuit is a big issue in LED related industries.